Binder for patching veneers



Patented July 1, 1941 UNITED "STATES PATENT OFFICE BINDER FOR PATCHING VENEERS v I James V. Nevin, Aberdeen, Wash.

No Drawing.

Application February 26, 1938 Serial No. 192,790 I 2 Claims.

v the hot-press process wherein a thermo-setting resinoid binder coated on the core ply is converted by the application of heat and pressure in the press into an insoluble and infusible bond integrally uniting the core ply with the veneer sheet.

Since the resulting compressed plywood panel may have defects in the surface veneers thereof, such as pitch pockets, knots, stains and the like, it has become the practice in the plywood industry to cut out these defects from the surface veneers of the finished panels and to'glue patches or pieces of wood inthe place of the cut-out portions. After the panel has been sanded, these inserted patches are practically invisible and present a clear surface on .the panel.

tions as the thermo setting bonding agent used for uniting the veneer sheets.

In preparing the binder of this invention, urea is dissolved in an aqueous solution of formaldehyde. Water-resisting agents, such as cresylic acid or xylenol are added to the mixture of urea and formaldehyde. These agents are used in small amounts. A'n alkaline condensing agent is then incorporated into the mixture and the mass is heated under reflux conditions to temperatures below the boiling point of water. It is desirable to insert a plasticizer, such as glycerol or a glycol,-

into the reacting mass. Buffers or stabilizers, such as mono and tribasic sodium phosphates; are also desirable to aid in maintaining the reaction product in colloidal solution.

The reaction is allowed to proceed-until a partial condensation between the urea and the formaldehyde is obtained. This condensation product .must be retained in the hydrophilic colloidal stage, and therefore the reaction is arrested by the addition of a solubilizing agent, such as so- In the usual cold glue process of making plywood wherein the cores and veneer sheets are bonded together by adhesive that sets in the cold, without requiring the use of hot presses, the gluing of patches into the veneer sheets is relatively simple, since cold setting glues can be used. However, in-the patching of outdoor plytion of the humidifying or seasoning treatment" According to this invention, a synthetic resinoid binder'capable of cold setting is provided to form an infusible and insoluble bond permanently securing a patch to a surface veneer sheet of a .plywood panel. The binder has almost'the same gluing properties and resistance to weather condidium borate.

syrupy reaction product obtainable by the above described process is then smeared in the hole on v the plywood panel and the patch pressed into the hole. The phosphoric acid will cause the reaction product to set into a hydrophobe condition. The set material is insoluble and infusible.

If desired, the syrupy liquid condensation prodnot can be admixed with wood flour or other filler to form a paste. This paste can be smeared into the reces or hole cut in the plywood panel'for receiving the patch.

The binder is substantially colorless and does not stain the wood. It has an adhesive strength equivalent to the strength of the bonding material used for uniting the plies of wood and equally resistant to moisture and weather conditions.

It is then an object of this invention to prepare a weatherproof cold setting adhesive for patching plywood veneers.

Another object of this invention is to provide a synthetic resinoid binder capable of being set to form an insoluble and infusible material without the aid. of heat.

Another object of this invention is to provide a hydrophiliccolloidal solution of a partially'conof from 62 to 65%.

\ a hydrophilic colloidal solution of a modified urea partial condensation product that contains a solubilizing agent forpreventi-ng setting of the resin until a mineral acid setting agent is'incorporated into the resin. c Other and further objects of the'invention will become apparent to those skilled in the art from the following example which illustrates a pre-" ferred specific embodiment of the invention. It should be understood that the example is in-'- tended to describe the invention specifically and that the invention is not limited to the specific details givenin the example.

The following formula illustrates the ingredi ents of a hydrophilic colloidal solution of a resinoid binder prepared from urea,- formaldehyde,

xylenol are condensed with the aid of the ammonia condensing agent to form the resin in a hydrophilic condition. In other words, the condensation is not carried on to completion to form an insoluble product.

The presence of the glycerol and the sodium phosphate salts in the reaction mass stabilizes the product. The salts also act as buffers to control the hydrogen ion concentration so that an insoluble material is not obtained. The glycerol renders the final product flexible. v v

The cresylic acid-or xylenol increases the water-resistant and water-repellent properties of the resin. The sodium borate acts as a solubilizer to prevent the formation of a rubbery mass upon standing of the solution.-

cresylic acid or xylenol in the presence of an; I

alkaline condensing agent. .The formula contains other ingredients imparting desired characteristi'cs to the product, as will be hereinafter described.

Urea Formaldehyde, '37 aqueous solution i 4750 Cresylic acid, 3. P 210-216" C.

,or i7!) xy1eno1, B. P. 210-225" C. r e Ammonia, 28% aqueous solution :56

Sodium borate 28' Glycerol '50 Sodium phosphate (monobasic) 3 Sodium phosphate (tribasic)' 3 1 The urea is added to the formaldehyde solu- L tion and dissolved therein by the aid of a gentle heat. The cresylic' acid or xylenol is next added to the mixture of urea and formaldehyde. The

'mass is thoroughly agitated untllswell mixed. The ammo nia, glycerol, monobasic sodium phosc phate' and tribasic sodium-phosphate arernext added to the reaction ingredients and the entire mass is heated under reflux conditions until the cally without the application of further heat for about minutes. During this exo-thermic re action period; the temperature will gradually rise to 206 or 208 degrees F. 7 v

The reaction is then continued for at least 3.

"" temperat ure reaches 198 to 200 degrees F. The l reaction is then allowed to proceed exo-thermi- ,180 to 200 degrees F. for a Isuflicient length of;

time to obtain a syrupy mass, which has a density of about 29-to 30 degrees l" The urea, formaldehyde and cresylic acid,- or

Be. and a solid content hyde, a soluble borate, a polyhydric alcohol The resulting solution is quite stable and may be kept indefinitely. If desired, 500 parts of the thus. obtained colloidal solution may be admixed with 30 parts of wood flour or fine sawdust to prepare a paste.

A setting or hardening'agent composed of a 35 to 50% solution of phosphoric acid and water is next made. up. The phosphoric acid solution is painted on the patch or edges of the veneer sheet surrounding the hole or recess, and this hole or recess is then coated throughout with the resin solution .or with the paste of the resin solution containing the sawdust or wood flour.

The patch is then pressed into the hole in the veneer surface while the excess binder solution is extruded around the edges of the patch. In a short time, the phosphoric acid will harden or set the resin solution into an iniusible and insoluble hydrophobe permanently uniting the patch with the veneer.

Other strong though the phosphoric acid is preferable.

After the resin has set .to bond the patch and .veneer, the panel surface can be sanded smooth.

The resulting surface will be clear and uniform, with the edges of the patch substantially invisible due to the lack of color of the set resin.

1 an aware that numerous details of the procpartial condensation product "of a reaction between 1700 parts of urea and parts cresylic acid with 4750 parts of 37% formaldehyde in the presence of small amounts of ammonia, sodium phosphate and glycerine. v 2. An adhesive adapted for cold setting with a mineral acid into an infusible water resisting resinous-mass comprising an aqueous dispersion of a resin derived from a simultaneous partial condensation of urea and a cresol with formaldeplasticizer and a soluble phosphate.

mineral acids might be used as hardening agents in place ofphosphoric acid, al-

JAMES v. ,NEVIN. f 

